1. Technical Field
This invention relates generally to heating appliances such as hot water heaters and, more particularly, to a thermal baffle located within the heater.
2. Background Art
In the prior art, a storage tank water heater replaces hot water withdrawn from the top of the tank with cold water delivered at the bottom of the tank. Because typical tank heating elements cannot heat the water as fast as it is withdrawn, cold water will eventually fill the tank. Even before the tank is filled with cold water, the incoming cold water mixes freely with the heated standing water in the tank thereby causing deterioration of the tank's water temperature. This mixing is partially the result of the currents generated by the inward flow of cold water, by the outward flow of hot water, and by the convection thermal currents established within the tank.
Because of this mixing, hot water delivered by a typical hot water heater will gradually decrease in temperature while water is being withdrawn, only a small amount of high temperature water is delivered relative to the tank's total capacity. The hot water volume delivered to the outlet above a specified temperature can obviously be extended by increasing the size of the tank or by increasing the heat input of the heating elements. The temperature of hot water at the outlet can also be maintained by preventing the mixing of hot and cold water within the tank.
Attempts have been made in the past to contain and control the mixing of hot and cold water by providing separate chambers within the tank for cold and hot water. Miller U.S. Pat. Nos. 2,833,273 and 3,244,166 employ separate chambers within the tank at the inlet. Gulick U.S. Pat. No. 2,207,057 uses a small baffle over the inlet to control mixing. Fox U.S. Pat. No. 787,909 shows the use of a movable barrier.
In substantially different constructions employing the concept of compartmentalization, Jacoby U.S. Pat. No. 2,625,138 divides the tank into a plurality of separate vertical layers by using numerous horizontal baffles and Pruitt U.S. Pat. No. 2,311,469 shows a fuel burner in which several secondary combustion chambers stratify the water in the storage tank.
While these prior art designs tried to reduce flow created by the usual high velocity of incoming cold water and tried to separate hot and cold water layers, none have taken note of the existence of possible convection currents and, thus, none limit the formation of these thermal currents in the tank and preserve the smooth horizontal boundary layer between hot and cold water within the tank. Further, these convection thermal currents are believed to flow primarily along the smooth side surfaces of the tank and are enhanced by the smooth inner surface of the curved top, the "domed" top being common in pressure tanks because of their structural strength. These closed loop currents greatly enhance the mixing of hot and cold water and heretofore no attempt has been made to stop mixing caused by these currents.